May 8, 2019
University of Michigan
A new study provides the first
evidence of transitive inference, the ability to use known relationships to
infer unknown relationships, in a nonvertebrate animal: the lowly paper wasp.
A new University of Michigan
study provides the first evidence of transitive inference, the ability to use
known relationships to infer unknown relationships, in a nonvertebrate animal:
the lowly paper wasp.
For millennia, transitive
inference was considered a hallmark of human deductive powers, a form of
logical reasoning used to make inferences: If A is greater than B, and B is
greater than C, then A is greater than C.
But in recent decades,
vertebrate animals including monkeys, birds and fish have demonstrated the
ability to use transitive inference.
The only published study that
assessed TI in invertebrates found that honeybees weren't up to the task. One
possible explanation for that result is that the small nervous system of
honeybees imposes cognitive constraints that prevent those insects from
conducting transitive inference.
Paper wasps have a nervous
system roughly the same size -- about one million neurons -- as honeybees, but
they exhibit a type complex social behavior not seen in honeybee colonies.
University of Michigan evolutionary biologist Elizabeth Tibbetts wondered if
paper wasps' social skills could enable them to succeed where honeybees had
failed.
To find out, Tibbetts and her
colleagues tested whether two common species of paper wasp, Polistes
dominula and Polistes metricus, could solve a transitive inference
problem. The team's findings are scheduled for online publication May 8 in the
journal Biology Letters.
"This study adds to a
growing body of evidence that the miniature nervous systems of insects do not
limit sophisticated behaviors," said Tibbetts, a professor in the
Department of Ecology and Evolutionary Biology.
"We're not saying that
wasps used logical deduction to solve this problem, but they seem to use known
relationships to make inferences about unknown relationships," Tibbetts
said. "Our findings suggest that the capacity for complex behavior may be
shaped by the social environment in which behaviors are beneficial, rather than
being strictly limited by brain size."
To test for TI, Tibbetts and
her colleagues first collected paper wasp queens from several locations around
Ann Arbor, Michigan.
In the laboratory, individual
wasps were trained to discriminate between pairs of colors called premise
pairs. One color in each pair was associated with a mild electric shock, and
the other was not.
"I was really surprised
how quickly and accurately wasps learned the premise pairs," said
Tibbetts, who has studied the behavior of paper wasps for 20 years.
Later, the wasps were
presented with paired colors that were unfamiliar to them, and they had to
choose between the colors. The wasps were able to organize information into an
implicit hierarchy and used transitive inference to choose between novel pairs,
Tibbetts said.
"I thought wasps might
get confused, just like bees," she said. "But they had no trouble
figuring out that a particular color was safe in some situations and not safe
in other situations."
So, why do wasps and honeybees
-- which both possess brains smaller than a grain of rice -- perform so
differently on transitive inference tests? One possibility is that different
types of cognitive abilities are favored in bees and wasps because they display
different social behaviors.
A honeybee colony has a single
queen and multiple equally ranked female workers. In contrast, paper wasp
colonies have several reproductive females known as foundresses. The
foundresses compete with their rivals and form linear dominance hierarchies.
A wasp's rank in the hierarchy
determines shares of reproduction, work and food. Transitive inference could
allow wasps to rapidly make deductions about novel social relationships.
That same skill set may enable
female paper wasps to spontaneously organize information during transitive
inference tests, the researchers hypothesize.
For millennia, transitive
inference was regarded as a hallmark of human cognition and was thought to be
based on logical deduction. More recently, some researchers have questioned
whether TI requires higher-order reasoning or can be solved with simpler rules.
The study by Tibbetts and her
colleagues illustrates that paper wasps can build and manipulate an implicit
hierarchy. But it makes no claims about the precise mechanisms that underlie
this ability.
In previous studies, Tibbetts
and her colleagues showed that paper wasps recognize individuals of their
species by variations in their facial markings and that they behave more
aggressively toward wasps with unfamiliar faces.
The researchers have also
demonstrated that paper wasps have surprisingly long memories and base their
behavior on what they remember of previous social interactions with other
wasps.
The other authors of the
new Biology Letters paper -- Jorge Agudelo, Sohini Pandit and Jessica
Riojas -- are undergraduates.
The work was supported by the
National Science Foundation and the Doris Duke Conservation Scholars Program at
the University of Michigan, funded by the Doris Duke Charitable Foundation. All
experiments complied with the laws of the United States and international
ethical standards.
Story Source:
Materials provided by University of Michigan. Note: Content may be edited
for style and length.
Journal Reference:
Elizabeth A. Tibbetts, Jorge
Agudelo, Sohini Pandit, Jessica Riojas. Transitive inference in Polistes
paper wasps. Biology Letters, 2019; 15 (5): 20190015 DOI: 10.1098/rsbl.2019.0015
